1. Field of the Invention
The present invention relates to a semiconductor device provided with a power semiconductor element and its production method.
2. Description of the Related Art
For example, a semiconductor device having a power semiconductor element such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is known to have a structure that a wiring board on which a semiconductor element is mounted is fixed to a metallic base substrate for heat-dissipating, and the periphery of the semiconductor element is covered with a frame. A gel-like resin layer is formed on a lower area within the frame, and a sealing resin layer is formed on the gel-like resin layer. One end of an externally leading terminal is connected to the wiring board, and the other end of the terminal is externally protruded through the gel-like resin layer and the sealing resin layer.
But, such a semiconductor device has a tendency that the gel-like resin layer charged into the frame is expanded with heat generated from the semiconductor element. With the expansion of the gel-like resin layer, a force of pulling upward is applied to the externally leading terminal, and a crack is easily produced in a joint portion for joining the wiring board and the externally leading terminal.
There is proposed a structure that a space is formed above the gel-like resin layer (e.g., JP-A 6-89946(KOKAI)). According to this structure, when the gel-like resin layer is thermally expanded, the expansion can be absorbed by the space, and a tensile stress applied to the externally leading terminal can be eased.
But, when the device is used with a bus bar connected to an end of the externally leading terminal which is externally protruded, vibrations transmitted from the bus bar to the externally leading terminal have a tendency to cause a crack in the joint between the wiring board and the externally leading terminal, or decreases a joint strength. As a result, the externally leading terminal is easily peeled from the wiring board, and the electrical connection between the externally leading terminal and the wiring board is degraded, resulting that the semiconductor device malfunctions.